The present invention generally relates to a motor vehicle and, more particularly, to a catalyst for purifying exhaust gas of the motor vehicle which has excellent heat resistance, and to a method of manufacturing the catalyst.
Recently, in response to higher output of an automotive engine and improvement of mileage or exhaust emission properties, there is a demand for higher heat resistance of a catalyst for purifying exhaust gas.
Thus, for example, Japanese Patent Publication No. 62-14338 published in 1987 proposes a catalyst for purifying exhaust gas, in which slurry formed by mixing at least one of cerium, zirconium, iron and nickel, at least one of neodymium, lanthanum and praseodymium and at least one of platinum, palladium and rhodium with active alumina is wash coated on the surface of a catalyst carrier.
However, the known catalyst has a drawback that since such catalyst elements as platinum and palladium are contained together on the catalyst carrier, both of the elements are alloyed by heat of exhaust gas, thereby resulting in deterioration of performance of the catalyst. Furthermore, in such catalyst, sintering of platinum takes place due to heat of exhaust gas, thus resulting in deterioration of performance of the catalyst.
Moreover, in such catalyst, since cerium has not only a function of improving purification performance of the catalyst but also the characteristic of deteriorating due to heat, zirconium having excellent heat resistance is contained in the catalyst in order to prevent this thermal deterioration of cerium.
However, since the cerium, zirconium and other elements are simply wash coated on the surface of the catalyst carrier in the form of a slurry mixture the atoms of zirconium are not in close enough relationship to the cerum atoms to sufficiently prevent thermal detrioration of cerium.
Therefore, such a catalyst has the disadvantage of low heat resistance because platinum, palladium and cerium are likely to deteriorate due to heat.